1. Field of the Invention
The present invention relates to a method of manufacturing an ink jet recording head for discharging droplets.
2. Description of the Related Art
An ink jet recording head used in an ink jet recording system (liquid jetting recording system) incorporates several microscopic recording liquid discharge ports, liquid passages and liquid discharge pressure generating portions which are formed in a part of the liquid passages. Further, in order to obtain a high quality image by this ink jet recording head, droplets of recording liquid (ink) are always discharged from the respective discharge ports, desirably by one and the same volume at an equal discharge speed.
As a method which can satisfy the above-mentioned desire, the specification of U.S. Pat. No. 5,218,376 discloses a method in which air bubbles are formed in ink by generating thermal energy in ink discharge pressure generating elements (electrothermal transducer elements), and the thus formed air bubbles are communicated with the ambient air so as to discharge the ink droplets. In an ink jet recording head which can achieve the above-mentioned method, the shorter the distance (which will be hereinbelow referred to as “OH distance”) between each of the electrothermal transducer elements and the associated discharge port, the more preferable the function. Further, in the methods including the above-mentioned method, since the OH distance substantially determines a discharge volume, it is required to set the OH distance to a precise and reproducible value.
Conventionally, a method of manufacturing ink jet recording head disclosed in the specification of U.S. Pat. No. 5,478,606 has been known. In this method, an ink passage pattern is formed on a substrate formed therein with ink discharge pressure generating elements with the use of dissoluble resin. Thereafter, coating resin containing solid-like epoxy resin is dissolved in a solvent, and is then coated over the dissoluble resin layer (solvent coating), and accordingly, a coated resin layer serving as an ink passage wall is formed on the dissoluble resin layer. After discharge ports are formed in the coated resin layer at positions just above the ink discharge pressure generating elements, the dissoluble resin layer is eluted. With this method, the distance between each of the ink discharge pressure generating elements and the associated discharge port can be set to a reproducible value with a relatively high degree of accuracy, thereby it is possible to manufacture an ink jet recording head capable of high quality recording. Further, in this method, the manufacturing process can be shortened, thereby it is possible to obtain an inexpensive and reliable ink jet recording head.
Further, there has been an increased demand for further enhancing the throughput of ink jet recording apparatuses in view of the market for digital cameras. As one of methods for satisfying this demand, there may be considered such a method that several discharge ports are densely arranged in a sub-scanning direction. In this case, it is required to shorten the horizontal distance (which will be hereinbelow referred to as “OC distance”, refer to FIG. 3) between a shoulder part at an end of the ink passage pattern and a position where a discharge port is formed, in dependence upon a layout of the discharge ports.
However, even though this distance is shortened, the opening diameter of the discharge port is not changed, and accordingly, the distance h shown in FIG. 3 becomes shorter. By this reason, in the method disclosed in the specification of the U.S. Pat. No. 5,478,606, irregularity is present more or less on the outer surface of a coated resin layer around an end of the passage pattern. Thus, should the distance h be excessively short, the discharge ports would be formed in the zone where the irregularity is present.
As a result, the reproducibility of the OH distance for each of the discharge ports is lost, and as well the OH distance at the peripheral edge of the respective ones of the discharge ports becomes uneven, depending upon a position. Thus, there has been offered such a risk that the discharge volume and a discharge direction are dispersed among the discharge ports or the recording heads.